Gaseous laser cooling system

ABSTRACT

A system for the removal of thermal energy from nonmetallic material which forms the boundary of a gaseous laser.

United States Patent William J. Schade J r.

Tustin, Calif.

Feb. 3, 1969 Jan. 12, 1971 to the United States of America as represented by the Secretary of the Navy Inventor Appl. No. Filed Patented Assignee GASEOUS LASER COOLING SYSTEM 9 Claims, 2 Drawing Figs.

US. Cl 165/ 156, 313/44; 331/945; 165/180 Int. Cl. F28d 7/00 Field ofSearch 165/156,

163, 184, 133; 313/44; 331/945, (Inquired)(Bauer Digest); 330/4.3(lnquired) References Cited UNITED STATES PATENTS 7/1938 Goddard 165/180X 6/1942 Rogers 165/184X 4/1960 Wertman... 313/44X 3/1966 Welton 330/43 5/1969 Bottum 165/156X Primary Examiner-Martin P. Schwadron Assistant Examiner-Theophil W. Streule Att0rneysEJ. Brower and J .M. St. Amand ABSTRACT: A

system for the removal of thermal energy from nonmetallic material which forms the boundary of a gaseous laser.

OURCE Q PATENTED. JAN 1 2 ml FIGJ FIG.2

WILLIAM J. SCHADE JR INVENTOR.

ATTORNEY GASEOUS LASER coouno SYSTEM The invention herein described may be manufactured and used by or. for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

BACKGROUND OF THE INVENTION Recent advances in laser technology make'use of gaseous lasers, such as CO lasers, practical for communications. Cooling of the laser tube is an essential requirement for most laser applications. Communication applications of gaseous CO lasers require highly stable, single frequency oscillation, and this will depend greatly on the temperature stability of the laser tube which is made of glass or fused silica. Higher gain (radiated intensity) can be achieved in a laser with reduced operating temperatures.

Previously, pipes and laser tubes of nonmetallic materials such as Corning Pyrex glass, Corning Vycor', fused silica, or quartz were enclosed in a cylinder so thatwater or some suitable coolant could be circulated around the outside of the inner tube whichcontained the heat source. Typically, the source of heat is an electric discharge in a gas to produce an amplifying medium for use in a laser. 1

Previous methods-depended on the thermal conductivity, heat capacity, and the volume rate of flow of the coolant. Water is the commonest coolant, but it has a relatively low thermal conductivity. The large volumes generally used for the cooling chamber, between the inner and outer tubes, result in a reduced rate of flow of the coolant and increased temperatures at the outer wall of the inner tube. The flow pattern is nonuniform around the inner tube so a nonuniform temperature distribution-is established resulting in the inner tube being distorted unevenly.

The present invention is for the removal of thennal energy (heat)from a nonmetallic material which forms the boundary of a source of thermal energy as in a gaseous laser tube.

The use of high thermal conducting materials to transport heat to the coolant which has high thermal capacity, and the use of higher volume flow-rates of coolant through the system provides a lower steady-state temperature for the boundary of the source of heat, and also provides on the outer boundary of the nonmetallic' enclosure a uniform temperature distribution which is necessary for mechanical stability in laser applications which require stable oscillation frequencies.

Other objects and many of the attendant advantages of this invention will become readily appreciated I as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:

FIG. 1 is a sectional illustration of a laser tube cooling system of the present invention.

FIG. 2 is an illustration taken along line 2-2 of FIG. 1.

This invention provides conductive cooling of nonmetallic materials in the following manner and as depicted in FIG. 1 of the drawing. A source of thermal energy such as a gaseous laser located within tube 12 must be dissipated to avoid overheating the source and the boundary of the container. Nonmetallic boundary 12 is typically a glass, quartz, or fused silica pipe or tube which contains the source of thermal energy and separates laser electrodes for an electric discharge in a gas. The geometry, and dimensions of tube l2-are determined by the specific application. A screen or mesh 14 which is in contact with the outer boundary of tube 12 is of material having a high thermal conductivity such as copper, for example. A plane sheet of screen mesh 14 is wrapped tightly around tube 12 and the edges laced together where they meet providing a conductive jacket which also gives added strength about tube 12. Bonding mixture 16 composed of material having a high thermal conductivity is used to bond mesh 14 to the outside of tube 12. The composition of bonding mixture 16 is a high concentration of powdered material (such as Al, 0 for dielectric ample) mixed in a vehicle such as paint or varnish (General Electric 0 7031 adhesive and Insulating Varnish, for example) which can be spread over and through conducting mesh 14. A length of copper tubing 17 is wrapped around the tube and mesh assembly and is held in contact with mesh 14 and bonding mixture 16 by an adhesive material 18 which is also a good thermal conductor (such as Devcon F-'2which is 80 percent aluminum and 20 percent plastic). The coolant 20 such as water, flows into the copper tubing at 22 and out at 23. Copper tubing 17 is wound about tube 12 as close or as far apart as desired. In operation, heat from the source at 10 is conducted through the tube 12 into the copper mesh 14 and bonding mixture 16. Mesh 14, bonding mixture I6 and adhesive material 18 conduct the heat to copper tubing I7. The coolant 20 flowing through copper tubing 17 rapidly and continuously transports the heat away from the system. This system has a dual purpose. When the copper tubing I7 is wrapped around a cylinder tube 12 in the fonn of a coil, a current can also be passed through coil 17 to establish an internal magnetic field for influencing the laser. This is done when bonding mixture 16 is a dielectric and does not electrically connect copper tubing 17 with the copper screen or mesh I4.

Where tube 12 is of irregular shape, copper screen or mesh 14 can readily be formed about such irregular shape in thermal contact with the surface of the glass tubing.

As an alternative method of construction, copper foil rather than a mesh or screen 14 can be adhered. to the glass tube wall 12 with a thin film of adhesive and copper tubing 17 for coolant 20 can be soldered or bonded to the foil as desired.

I claim:

1. The combination of a gaseous laser tube having a cooling system integral therewith for removal of thermal energy and provide an outer boundary of uniform temperature distribution necessary for mechanical stability in laser applications which require stable oscillation frequencies, comprising:

a. a tube of dielectric material which houses and forms the boundary of a high thermal energy laser source, said dielectric material being selected from glass, quartz and fused silica;

b. a sheet of highly thermally conductive metallic material wrapped tightly about and covering the outer boundary of said dielectric tube;

c. said sheet of highly thermally conductive metallic material bonded to the outside of said dielectric tube with a high thermally conductive bonding material;

d. a length of coolant tubing having goodthermal conductivity wrapped about said tube covered with said sheet of highly thermally conductive metallic material and said bonding material; 7

e. said coolant tubing being fastened about said dielectric tube and metallic wrapping with an adhesive material of good thermal conductivity; and

f. said coolant tubing capable of having high volume flow of coolant liquid passed therethrough for rapidly arid continuously conducting heat away from the system and providing a uniform temperature distribution on said tube of dielectric material.

2. A system as in claim 1 wherein said sheet of highly thermally conductive metallic material is a metal mesh.

3. A system as in claim 1 wherein said sheet of highly thermally conductive metallic material is a metal foil. 1

4. A system as in claim 1 wherein said high thermally con ductive bonding material is Al, 0 mixed with'an insulating adhesive.

5. A system as in claim I wherein said highly thermally conductive material is copper dust mixed with and insulating varnish.

6. A system as in claim 1 wherein said coolant tubing is made of copper.

7. A system as in claim 1 wherein said coolant tubing is fastened about said tube with an adhesive of 80 percent aluapplications or copper dust for metallic -applications,.for exminum dust and 20 percent plastic.

fluencing the laser within said dielectric tube.

9. A system as in claim 1 wherein said sheet of highly thermally conductive metallic material is of copper. 

2. A system as in claim 1 wherein said sheet of highly thermally conductive metallic material is a metal mesh.
 3. A system as in claim 1 wherein said sheet of highly thermally conductive metallic material is a metal foil.
 4. A system as in claim 1 wherein said high thermally conductive bonding material is A12 O2 mixed with an insulating adhesive.
 5. A system as in claim 1 wherein said highly thermally conductive material is copper dust mixed with and insulating varnish.
 6. A system as in claim 1 wherein said coolant tubing is made of copper.
 7. A system as in claim 1 wherein said coolant tubing is fastened about said tube with an adhesive of 80 percent aluminum dust and 20 percent plastic.
 8. A system as in claim 1 wherein said coolant tubing coiled about said tube is electrically conductive and said bonding material is dielectric, and a current passed through said coil of coolant tubing will establish an internal magnetic field for influencing the laser within said dielectric tube.
 9. A system as in claim 1 wherein said sheet of highly thermally conductive metallic material is of copper. 